Nanospot welder and method

ABSTRACT

A method and apparatus for assembly of small structures is disclosed. The present invention discloses electron beams created from one or more nanotips in an array operated in a field emission mode that can be controlled to apply heat to very well defined spots. The multiple electron beams may be generated and deflected and applied to electron beam heating and welding applications.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention claims priority to the following:

Provisional Patent Application Ser. No. 60/469,381, entitled “CARBONNANOTUBE HIGH CURRENT DENSITY ELECTRON SOURCE,” filed on May 9, 2003;

Provisional Patent Application Ser. No. 60/508,815, entitled “NANOSPOTWELDER AND METHOD,” filed on Oct. 3, 2003; and

Provisional Patent Application Ser. No. 60/549,200, entitled “NANOSPOTWELDER AND METHOD FIELD OF THE INVENTION,” filed on Mar. 2, 2004.

TECHNICAL FIELD

The present invention relates in general to the creation of weld jointsin small structures.

BACKGROUND INFORMATION

1. Electron Sources

Researchers have been working on developing electron sources usingcarbon nanotubes (CNTs) for about ten years. One of the earliestreferences to this work is the patent of Keesmann et al. (U.S. Pat. No.5,773,921). Some examples of the applications of using CNT electronsources are for displays (field emission displays and cathode ray tubesare two examples), e-beam lithography, x-ray sources and microwavedevices (traveling wave tubes, klystrons, magnetrons, etc.). Some ofthese applications require high currents and high current densities, inthe range of 1-100 Amps/cm², in both pulsed and continuous wave (CW) ordirect current (DC) modes. Many of these applications requiring highcurrent densities are now being met using hot (thermal) cathodes ofvarious types. All of these hot cathodes require power to heat thecathode and maintain its temperature in the range of 1000° C.

Other cold cathode technologies exist, but many of these requirefabricating arrays of micron-size microtips. These are expensive tofabricate and not very reliable in extreme environments. This isevidenced by the fact that several companies that have made an effort tomake microtip-based field emission displays have recently abandonedtheir efforts. Trying to incorporate microtip cathodes into microwaveand x-ray devices has also met with limited success. On the other hand,carbon nanotube electron sources have been made with very inexpensiveprocesses (such as printing or dispensing) over large areas.

Gated microtip electron sources, despite their weaknesses, did have anadvantage of generating high current densities. (SRI Internationalclaimed 11.6 Amps/cm² at 250V, “Application of Field Emitter Arrays toMicrowave Power Amplifiers,” D. R. Whaley et al., Abstracts of theInternational Vacuum Electronics Conf, May 2-4, 2000, Monterey, Calif.;NEC Corporation claimed 1.27 Amps/cm² from a Si microtip gated device“Field-Emitter-Array Cathode-Ray-Tube (FEA-CRT),” K. Konuma et al., SID99 Digest p. 1151, 1999; Extreme Devices claimed 4 Amps/cm² using whatthey claim as “diamond cathode technology,” Spec sheet for E-ChipED138-250 dated March 2003—Rev. 2; see also “A Micromachined VacuumTriode Using a Carbon Nanotube Cold Cathode,” C. Bower, et al., IEEETrans on Electron Devices, Vol. 49, No. 8, p. 1478, August, 2002.)

The literature of carbon nanotube electron sources has examples ofachievement of a few Amps/cm². (E.g., claim of 4 Amp/cm² with totalcurrent of only 0.4 mA in “Large current density from carbon nanotubefield emitters,” W. Zhu et al., App. Phys. Let. Vol. 75, No. 6, p. 873,August, 1999.) Most of these claims were sources operated in a diodemode (ungated, anode and cathode only) and thus are of limited use forthe applications of interest. What is needed is a gated electron sourceusing carbon nanotube cathodes that can achieve high current densities.Some attempts have been made to make a gated source using carbonnanotubes (one example is D. S. Y. Hsu, et al., “Integrally Gated CarbonNanotube-on-Post Field Emitter Arrays”, App. Phys. Lett., Vol. 80., p118, 2002). The best that has been achieved is on the order of 0.1Amps/cm².

There are a couple of reasons why gated, high current density electronsources have not been made. The CNT cathodes are not regular arrays ofnanotubes that are positioned in an exact formation and aligned in anexact direction. Instead, they are irregularly positioned and randomlyoriented. In some cases, the alignment is preferential in a certaindirection; but, unless the position and the alignment of the CNTs areengineered precisely, it will be difficult to design and engineer anoptimized gated structure such as is done for microtip sources. The lackof optimization leads to poor efficiency of the emitted electrons (manyof them strike the gate structure, creating heat that will ultimatelylead to device destruction) and poor use of cathode area (much of thearea is dedicated to gate structure and not CNT emitters). Many of thecarbon nanotubes are also not optimized for high current electronemission. They can unravel or become hot and disintegrate. Increasingthe density of carbon nanotubes is not a solution either because theyelectrically screen each other from the applied electric field needed toextract the electrons from the nanotubes (see Jean Marc Bonard et al.“Tuning the Field Emission Properties of Patterned Carbon NanotubeFilms,” Advanced Materials, 13, 184 (2001)). Thus, there is a need toincrease the means of increasing the current density of gated electronemission devices using CNT cathodes.

One means of increasing the current density is to use an approach thatis similar to what van der Vaart et al. have described in U.S. PatentApplication Publication US 2002/0053867 A1 (see also InternationalPublication Number WO 00/79558 A1). This approach is also described inpapers published in the SID literature (“Technology for the HoppingElectron Cathode,” P. J. A. Derks, et al., SID 02 Digest, p. 1396; “ANovel Cathode for the CRTs based on Hopping Electron Transport,” N. C.van der Vaart,” SID 02 Digest, p. 1392; “A Novel Electron Source forCRTs,” van der Vaart et al., Information Display, Vol. 18, No. 6, p. 14,June 2002).

In this Hopping Electron Cathode (HEC) approach, the electrons from athermal cathode are “condensed” by a funnel-shaped structure that iscoated with a layer of secondary electron emitter material. FIG. 1illustrates how this approach works. The electrons from a hot cathodeare extracted by use of a gauss electrode (grid) from the cathode andthen strike the funnel. Secondary electrons are generated when thevoltage of the electrode at the top of the funnel is sufficiently highenough (about 300-500V). Because the funnel surface is insulating andcharge conservation must be maintained, the current is neither amplifiednor degraded, but collected by the funnel to the opening at the end ofthe funnel. Using this approach, very high electron current densitiescan be emitted from the funnel opening, exceeding 1000 Amps/cm².

2. Welding

With smaller and smaller structures and assemblies required for manyapplications, there is a need for assembly and welding technologies forthe smaller structures. As just one example, there is a need for weldingfine hydrogen separation membranes into very small reactors(micro-reactors). There is also a need for heat treatment on a finescale and with high resolution. High throughput is also required forproduct manufacturing. There are several methods for welding two piecesof material together.

Contact welding (tack welding)—This involves forcing high current in ashort pulse though the two parts. Typically, the joint between the twoparts is highly resistive compared to the bulk of the materials and thisarea is heated rapidly by the pulse current. The temperature can rise tonear or over the melting point of one or more of the materials and abond is created between the materials. Typically, the size scale forthis type of welding is on the order of 1 mm or larger. In this case,both parts must be metallic.

Wire bonding—Wire bonding is similar to contact welding. Ultra-sound canbe applied in addition to high pulse current to create a bond. The sizescale is on the order of 0.1 mm and can be highly automated. This isgood for making interconnects to integrated circuits and printed circuitboards, but limited in making other assemblies.

Laser bonding—A laser can be focused to a small spot and create localheating to make a bond. Mirrors on micropositioners can direct the beamto many different spots. This approach is flexible but it is difficultto make a multibeam system to increase the throughput. In addition,metals reflect a large percentage of the light, decreasing theefficiency of the welder. The size of the spot is on the order of 0.1 mmto 0.01 mm.

Focused Ion Beam (FIB)—FIB systems are much like scanning electronmicroscopes (SEMs). FIBs can focus a beam to nano-scale sizes; 10nanometer features have been demonstrated. This approach can achieve thefine resolution required for many applications, but FIB machines areexpensive systems and the throughput is very low because only one beamis available to do all the machining. FIB systems are typically used formicromachining by etching material away and are not used for welding.

Electron beam welders or Scanning Electron Microscopes (SEMs)—Electronbeam welders use a electron gun to weld joints in a vacuum environment.Typically, the focus of the electron beam is 0.1 mm to 1.0 mm. SEMs canfocus to much finer resolutions, but typically have very small currents,not sufficient for welding or bonding. Both systems use only one beam toperform all the processes. The size of the beam (welding spot) and thethrough put of standard electron beam welders and SEM machines are notsufficient for many nanospot welding and heat treatment applications. Ane-beam welder is needed that can be sealed to an array for multibeamapproaches and also achieve small beam sizes.

It is therefore a desire to provide a nanospot welder and method thataddresses the need for assembly apparatus and methods for very smallstructures.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and aspects of the present inventionwill be best understood with reference to the following detaileddescription of a specific embodiment of the invention, when read inconjunction with the accompanying drawings, wherein:

FIG. 1 illustrates a prior art hopping electron cathode (HEC);

FIG. 2 illustrates a gated HEC;

FIG. 3 illustrates a graph of current versus hopping electron bladespotential;

FIG. 4 illustrates anode and grid currents allotted as a function of anextraction field;

FIG. 5 illustrates a HEC with electrostatic focusing elements;

FIG. 6 illustrates an image created by an electron beam using theembodiment illustrated in FIG. 5;

FIG. 7 illustrates an array of HEC sources;

FIG. 8 is a representative view of a nanospot welder;

FIG. 9 is an image of a CNT fiber on the end of an AFM tip;

FIG. 10 is a an image of a carbon nanotip on the end of a tungstenneedle;

FIG. 11 is a representative side view of a nanospot welder;

FIG. 12 is a representative view of another embodiment of a nanospotwelder utilizing a multiple electron beam;

FIG. 13 is a representative cross-sectional view of a gated CNT electronsource;

FIG. 14 is a representative view of another embodiment of the presentinvention;

FIG. 15 is an image of a result of using an embodiment of the presentinvention; and

FIG. 16 is an image of an array of HEC sources and a work piece isolatedin two separate chambers by the funnel array of the HEC source.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forthsuch as specific display configurations, etc. to provide a thoroughunderstanding of the present invention. However, it will be obvious tothose skilled in the art that the present invention may be practicedwithout such specific details. In other instances, well-known circuitshave been shown in block diagram form in order not to obscure thepresent invention in unnecessary detail. For the most part, detailsconcerning timing considerations and the like have been omitted in asmuch as such details are not necessary to obtain a completeunderstanding of the present invention and are within the skills ofpersons of ordinary skill in the relevant art.

Referring to FIG. 2, the funnel is two blades of alumina 201 that areshaped to form a slit funnel. A cylindrical funnel can also be used,such as described in the Philips papers.

FIG. 3 shows the efficiency of the HEC 204 vs. the blades 201 potential.The prior art literature mentions the potential on the funnel electrodesof nearly 500-700V is needed. However, it is seen that the potential of150-200V is good enough to force the electrons to come out from the slit202. The efficiency of the source (the ratio of emitted current from thecathode 204 to the current collected at the anode 203) increased from 0to about 67% when the potential on the funnel electrode was increased.The beam image on the phosphor screen 203 also changed: from a smallsingle spot at low voltage to a two-lobe structure at higher voltage onthe blades.

It should be noted that the current in the blade electrodes 201 was muchlower then the grid and anode currents. Furthermore, the anode currentcan be modulated with the bias on the funnel electrode. The modulationis linear with funnel potential from 0V to about 140V. Additionalexperiments showed that this modulation potential from 0 to 100% swingis roughly independent of the current that is delivered from thecathode/grid assembly (e-gun). In other words, the graph shows that the140V swing on the potential will modulate the current from the electrongun from 0 to 2.2 mA. If the grid voltage on the electron gun wasincreased, then the electron gun would be capable of emitting highercurrents (the grid current at 0V on the funnel electrode would behigher) and the anode current with 140V on the funnel electrode wouldalso be proportionally higher.

In FIG. 3, at zero potential on the funnel electrode, the entire cathodecurrent goes to the extraction grid. As the funnel electrode potential(HEC blade potential) increases, more of the emitted current iscondensed and passes through the funnel 202 and is then collected by theanode 203. Efficiency is the ratio of the anode current to the totalcurrent emitted from the cathode 204 and is plotted as a fraction100%=1.0 in the graph.

The graph in FIG. 4 measures the I-V curve at constant voltage on thefunnel electrode. The objective of this task is to obtain a peak anodecurrent of ˜25 mA in a pulse mode. The pulse width was 10 μs, frequency100 Hz, ballast resistor of 25 kOhm in series with the phosphor anode.The potential on the funnel electrodes was held at 500V constant and theextraction grid voltage in the electron gun 204 was ramped up.

In FIG. 4, the anode 203 and grid currents are plotted as a function ofthe extraction field generated between the cathode and the grid 204. Thefunnel electrode 201 potentials were held constant at 500V. Efficiencyis also plotted as the percentage of total emitted current from thecathode collected at the anode. A value of 35 on the plot corresponds to70% efficiency.

This shows that the current through the funnel 202 and collected at theanode 203 is about 30 mA. Since the gap 202 in the funnel is only 0.005cm×0.4 cm, then the current density of electrodes flowing through thegap is about 15 Amps/cm². The current along the length of the slit 202is not uniform, the current in the center is much higher because theelectron gun source is round and not rectangular. Thus the currentdensity in the center of the slit 202 is probably 30 Amps/cm² or higher.

A method of overcoming the inherent current density limitations of gatedelectron sources is performed using carbon nanotube emitters bycondensing the beam from a CNT gated electron source into a narrowerbeam of electrons. Current densities as high as 15 Amps/cm² weredemonstrated By making the funnel a cylindrical funnel and not the slit,it is expected that current densities as high as 1000 Amp/cm² can beachieved. This current can be modulated with voltages between 0 and150V; the current modulation is linear in proportion to the potential onthe funnel electrode. This was demonstrated by operating a test circuitas shown in FIG. 2 in a pulsed mode (duty factor of 0.1%). Similarperformance is expected with operating in a CW or DC mode.

The beam coming from the funnel can be accelerated, focused withelectrostatic or magnetic focusing elements or deflected usingelectrostatic or magnetic deflection elements similar to what is used instandard CRT electron guns. FIG. 5 shows how the electrostatic focusinglens 507, 508 can be used to focus the electrons coming through thefunnel.

FIG. 6 shows an image on anode 503 where the beam can indeed be focusedto a narrow beam using the focusing elements 507, 508.

Referring to FIG. 7, it is also possible to make an integrated array offunnels for pixilated electron sources. This array can be x-yaddressable. This can be done in a couple of ways. The electron sourcesbefore the funnel can be x-y addressed or a control line that also actsas the funnel electrode can be patterned on the exit side of the funnelarray. The funnel array can be made out of alumina, glass or otherinsulator. It can be coated with MgO in the funnel openings to improvethe secondary electron performance of the funnel. The funnel exit holescan be circular, rectangular or other shapes. The funnel array can thenbe placed on a patterned electron source (a CNT source is illustrated,but the source can be microtips, a thermal cathode, or other sources),the pattern of the electron source aligning with the openings (largeend) of the funnel. Each funnel in the array condenses the electronsthat enter it from the large opening. An unpatterned electron source mayalso be used if a flood of electrons is needed

It is also possible to make just a linear array of sources, similar towhat is shown in FIG. 7, but aligned only in one row. Each of thesesources can be independently controlled in intensity. The focus anddeflection of the each of the sources can be together (in tandem) orseparately. The openings of the sources can be as small as 0.5 micronsfor fine-focus x-ray sources or multibeam e-beam lithographyapplications. Display applications can have much larger dimensions. Thehopping electron cathode or funnel approach also has the advantage inthat the work piece and the electron source can be isolated from eachother by the funnel array. The holes of the funnel can be made verysmall (as small as 0.5 micron as noted earlier) so the opening areathrough the funnel array to the electron sources can be a very smallpercentage of the total array area. Gasses created in the work areawhere the electrons hit the work piece can be blocked from entering thearea of the electron sources, increasing the stability and life of theelectron sources. FIG. 16 shows the work piece in a separate chamberfrom the electron sources, separated by the funnel array. (The funnelarray can have as few as one funnel in principle.) Different vacuum orgas environments can be placed in each of the chambers. For example, astrong vacuum pump (not shown in FIG. 16) can be used to evacuate theelectron source chamber to a better vacuum than the work piece chamber(e.g. 10⁻⁷ Torr in electron source chamber and 10⁻³ Torr in work piecechamber). Different gas environments can also be used to in the workpiece chamber than in the electron source chamber. For example, a highpartial pressure of Ar gas can be used in the work piece chamber and ahigh partial pressure of H₂ gas can be used in the electron sourcechamber. Other gasses and arrangements are also possible. The smallopenings of the funnel will allow some gases to mix between the chambersbut this will be limited by the size of the openings and to a smallerdegree by the shape of the funnel. Small funnel openings and long,narrow funnels will limit the gas mixing between the two chambers.

The work piece is show in FIG. 16 without any support. In fact, supportswill be needed to control the gap (z direction) between the funnel andthe work piece and also to allow the work piece to move laterally withrespect to the funnel (x and y, y is out of the paper). These supportsare not shown to simplify the figure; these supports are well known inthe state of the art.

FIG. 8 is a representative view of a nanospot welder in accordance withan embodiment of the present invention. The nanospot welder includes amodified Atomic Force Microscope (AFM) or a Scanning TunnelingMicroscope (STM) machine to make a beam of electrons that areaccelerated at high energy in a beam to heat a small spot. Atomic ForceMicroscopes and Scanning Tunneling Microscopes are also described underthe term Scanning Probe Microscopes (SPM). The AFM or STM tip is not incontact with the work piece during the welding process. The tip isoperated in a field emission (FE) mode such that electrons are extractedfrom the tip. The electrons are accelerated to the work piece to locallyheat and bond material. The tip may remain stationary during the bondingprocess or it can be scanning. Before the bonding process, the tip maybe used in a AFM or STM mode to locate the bond site accurately. Whenthe bond site is located, the tip may be withdrawn to a distance andoperated in a field emission mode.

The expected operating mode of this device would be to place the weldertip a small distance away from the sample. These gap distances are onthe order of 10 nm to as large as 100 microns, depending on the spotsize of the beam required and how much voltage one would like to put onthe welder tip. Since the device operates in a diode mode (no gatestructure), the beam current, welder tip voltage and gap are variablesthat are interdependent. If the gap is 100 microns, then 1000V could beplaced on the welder tip to draw about 2 micro-Amps of current from thetip to the work piece. This creates a beam power of 2 mWatts and a localpower density of 100 Watts/cm2 for a spot size expected to be about 50microns in diameter. These numbers are estimates and serve only as adescription of the expected mode of operation. Smaller gaps may lead tolower voltage on the needle, but in turn may lead to smaller spot size.Even though the total power in the beam may decrease, the power densitymay not change nearly as much.

The tip can be coated with a carbon film to increase durability. The tipmay be a carbon-based microtip. Tips made of alloys or compounds ofcarbon are also good for this application. A carbon nanotube fiber canbe grown from the tip end of the microtip as described in (U.S. Pat. No.5,773,921). An image of a CNT fiber grown on the end of an AFM tip isshown in U.S. Pat. No. 6,146,227 and included as FIG. 9.

It is also possible to fabricate a smaller tip on the end of a largertip or needle. In the publication by S. D. Johnson et al. (“CarbonNanotips for Field-Emission Electron Guns” Abstracts of the 47^(th)International Conference on Electron, Ion and Photon Beam Technology andNanofabrication, Tampa, Fla., May 27-May 30, 2003, p274), a carbonnanotip is grown on the end of a tungsten needle. This is shown in FIG.10.

Referring to FIG. 11, the nanospot welder may include one tip or a gangof tips on a single or multiple boards. The gang of tips can be in anarray on a printed circuit board. Each tip can be independentlyaddressable in both gap (displacement) and/or voltage on the tip. Eitherone will regulate the current emitted from the tip. Driver chips mountedon the PCB can drive each tip individually or two or more in tandem. ThePCB is displaced from the work piece by a small gap that is controlledby supports and actuators on the work piece and PCB (not shown). The PCBand/or the work piece can be moved relative to each other in order toallow the tips to address the full area of the work piece. Current isdrawn from each of the tips by increasing the voltage to the tip of bychanging the gap of the tip to the work piece. The gap between the workpiece and each of the tips may be individually controlled.

FIG. 12 is a representative view of another embodiment of the nanospotwelder of the present invention. This embodiment of the nanospot welderincludes a multiple electron beam. In this embodiment, several electronbeams are used to provide heat treatment or to perform welding tasks.Typically, the beams would be in an array. The current and voltage ofeach beam may be independently controlled although the typical mode ofoperation would be to keep the beam voltage the same for each aridmodulate the current of each beam as a function of time and position ofthe beam on the work piece.

The beam current can be modulated by a control or extraction grid overthe cathode. The cathode can be thermal (hot cathode) or cold (microtipsor carbon nanotubes or photocathodes). The beam currents can also bepulse-width modulated to control the duty factor of the beam ON time.The electron source may be a hopping electron cathode using either athermal electron source or a cold electron source (including carbonnanotubes) to achieve electron source current densities as high as 15Amps/cm² or higher. The position of each beam can be controlled byelectrostatic deflection. An example of such a structure for a displayapplication is shown in FIG. 13, which also shows electrostatic focusingof the electron beam. A similar approach was taken for a display devicewas recently disclosed in “Flat CRT Display” and is incorporated intothis disclosure by reference to U.S. Pat. No. 6,411,020 andPCT/US99/01841-WO 99/39361. The beam focus can be controlled by therelative potential applied to focus electron and aperture electrodesrelative to the cathode and extraction grids.

The beams can also be controlled (deflected and focused) using magneticfields. This is not shown, but similar methods are used to control theelectron beams in cathode ray tubes (CRTs) used as TVs, scanningelectron microscopes and multiple-beam and projection e-beam lithographyapproaches (e.g., DiVa approach of Timothy Groves: T. R. Groves and R.A. Kendall; Journal of Vacuum Science and Technology, B16(6), November1998, p. 3168). Using a magnetic field parallel to the directed electronbeams as in the DiVa approach allows one to focus the beams to verysmall spots (sub-micron) at periodic distances away from the sourcewithout using electrostatic lenses, making the system fabrication muchmore simple. The magnetic fields can be generated using standardelectromagnets in a Helmholz coil configuration as described in mostelementary physics texts. It is also possible in the embodiments to movethe work piece during the welding process. The movement can becontinuous or stop-and-go, depending on the application.

Yet another approach to making a nanospot welder is to use an electrongun with a concentrator of electrons utilizing a mechanism of electronshopping over the surface of a funnel-shaped or tapered hole made in adielectric, where the electron drift toward the hole outlet ismaintained by applying an electric field oriented along the axis of thehole. Prior art of such an electron gun design includes, for example,patent application U.S. 2002/0053867, WO 00/79558, and WO 01/26131.

Referring to FIG. 14, the electric field is induced by applying apotential to a welded part that becomes an accelerating electrode and atarget at the same time. The energy of electrons is determined by thepotential on the target. It is possible to bring the target temperatureto a melting point or adjust the target temperature either by changingthe electron beam current, target potential, or use pulse-width or pulsefrequency modulation. More specifically, it is possible to bring thetarget temperature to a specified value by making a certain number ofelectron beam pulses.

Since the electrons diverge as they exit the hole, it is necessaryeither to place the welded part close to the hole outlet or use focusingelectrodes. FIG. 14 depicts a concept where no focusing electrodes areused, and spacers are used to ensure that melted metal does notinterfere with the dielectric concentrator. The concentrator may havethe hole of any geometrical shape, e.g., cone, square pyramid, orrectangular pyramid.

A part of the welder is an electron gun. The electron gun is a source ofelectrons, and it may be a gated source. It may be either a thermioniccathode or cold cathode that uses field emission of electrons. In thedescribed embodiment, a gated carbon nanotube cold cathode was used,which was capable of reaching up to 1 Amp/cm² of electron current. Withsuch an electron gun and a rectangular shaped hole in a ceramic electronconcentrator, the effect of melting a metal foil was achieved where thewelding spot has a diameter of nearly 50 microns. FIG. 15 shows thephotograph of the foil with a spot of melted and then solidified metal.

The spot size that can be achieved depends on the design of the nanospotwelder parts that, in turn, specifies an electron optics configuration.Also, the spot size can be changed by varying the hole exit size. It ispossible to make the size of the hole outlet of sub-micron dimensions.As in previous two concepts, it is possible to move the work pieceduring welding in a certain manner, either stop-and-go or continuously.

This concept can take a multiple-beam approach as well. A welding arraycan utilize either one electron gun with a mosaic concentrator, wherethe electron beam will split over multiple concentrators, or a multiplegun-concentrator system. A mosaic concentrator for a single-gun designcan be made of a single piece of dielectric, or a mosaic where seamsbetween parts are made in such a way that they do not result insignificant loss (or leak) of electron current. A multiple gun design isused where the beam configuration often needs to be changed, and/or thesystem is used for sub-millimeter (or larger scale), rather thensub-micron, welding.

From the foregoing detailed description of specific embodiments of theinvention, it should be apparent that a nanospot welder and method thatis novel has been disclosed. Although specific embodiments of theinvention have been disclosed herein in some detail, this has been donesolely for the purposes of describing various features and aspects ofthe invention, and is not intended to be limiting with respect to thescope of the invention. It is contemplated that various substitutions,alterations, and/or modifications, including but not limited to thoseimplementation variations which may have been suggested herein, may bemade to the disclosed embodiments without departing from the spirit andscope of the invention as defined by the appended claims which follow.

1. (canceled)
 2. (canceled)
 3. (canceled)
 4. (canceled)
 5. (canceled) 6.An apparatus comprising: a work piece; a printed circuit boardsupporting a plurality of electron beam sources; and circuitry foractivating the plurality of electron beam sources to each emit anelectron beam with sufficient energy to create a plurality of weldjoints on a the work piece positioned a distance from the printedcircuit board.
 7. The apparatus as recited in claim 6, wherein theelectron beam source is a scanning probe microscope.
 8. The apparatus asrecited in claim 6, wherein the electron beam source is an AFM microtipprobe.
 9. The apparatus as recited in claim 6, wherein the electron beamsource is a STM microtip probe.
 10. The apparatus as recited in claim 6,wherein the electron beam source is a hopping electron cathode.
 11. Theapparatus as recited in claim 6, wherein the work piece is movablerelative to the printed circuit board.
 12. The apparatus as recited inclaim 6, wherein the plurality of electron beam sources are activated inparallel.
 13. The apparatus as recited in claim 6, wherein the pluralityof electron beam sources are arranged in an array on the printed circuitboard.
 14. (canceled)
 15. (canceled)
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 17. (canceled) 18.(canceled)
 19. (canceled)